DESCRIPTION (Investigator's Abstract) The purpose of the proposed study is to examine the long-term structural and functional effects of cryotherapy as a treatment for severe retinopathy of prematurity (ROP). In the initial phase of the study, eyes with 5 contiguous or 8 total clock hours of stage 3 plus ROP, in 291 infants with birthweights less than 1251 g., were randomized to receive cryotherapy or no cryotherapy. Follow-up to age 12 months indicated that cryotherapy reduced the incidence of unfavorable structural outcome by 45.8 percent and the incidence of unfavorable visual acuity outcome by 37.8 percent. Based on the preliminary data, follow- up to age 42 months during Phase II of the study indicated that cryotherapy reduced the incidence of unfavorable structural outcome by 39.1 percent. As for vision, cryotherapy reduced the incidence of unfavorable resolution acuity by 21.4 percent, and by 19.7 percent when based on measurement of recognition acuity. The present study proposes to follow patients in the randomized group and a relatively small subgroup (67) of potentially high risk patients from the Natural History stud through age 10 years. to determine whether the reduction in the benefit of cryotherapy seen between ages 12 and 42 months continues into mid-childhood. Evaluation of the effects of cryotherapy will be based on examination findings in the posterior pole of the eye and on assessment of visual acuity, as in Phase II. In addition, a more complete evaluation of visual function will be conducted at age 9 years, through assessment of monocular contrast sensitivity, monocular color vision, and stereopsis, and at 10 years, through measurement of the extent of the visual field by Goldmann perimetry.